An arrayed waveguide grating type optical multiplexer/demultiplexer circuit can multiplex or demultiplex optical signals having different wavelengths, and therefore, it is used as an optical multiplexer or an optical demultiplexer for wavelength division multiplexing communications which enables transmission of a large amount of information. In order to miniaturize or mass-produce the arrayed waveguide grating type optical multiplexer/demultiplexer circuit, an input/output waveguide, a slab waveguide, and an array waveguide as constituent parts of the arrayed waveguide grating type optical multiplexer/demultiplexer circuit are formed on a waveguide substrate such as a silicon wafer, which is then cut out into optical chips including the arrayed waveguide grating type optical multiplexer/demultiplexer circuit.
In fabricating an arrayed waveguide grating type optical multiplexer/demultiplexer circuit in the prior art, rectangular regions 91 are frequently arranged on a circular silicon wafer 509, and then, an arrayed waveguide grating type optical multiplexer/demultiplexer circuit 202 is formed in the region, as illustrated in FIG. 9. This is because optical chips can be readily cut out from the rectangular region by a dicing saw. However, the arrayed waveguide grating type optical multiplexer/demultiplexer circuit has many curved portions, and therefore, many regions which cannot be effectively used remain within the rectangular optical chip. In this manner, the number of optical chips per waveguide substrate, that is, an optical chip yield rate is reduced, resulting in an increase in unit price of the optical chip.
On the other hand, Japanese Patent Application Laid-open No. 2002-250826 (“JP '826”) discloses an arcuate optical chip. As illustrated in FIG. 10, it is disclosed that arcuate regions 93 are arranged on a silicon wafer 510, and then, an arrayed waveguide grating type optical multiplexer/demultiplexer circuit 202 is formed in the region. More arrayed waveguide grating type optical multiplexer/demultiplexer circuits can be formed in the arcuate regions on the silicon wafer than in the rectangular regions, thereby increasing an optical chip yield rate.